Using arrival sequence access paths for database files

 

An arrival sequence access path is based on the order in which records arrive and are stored in a database file. For reading or updating, records can be accessed:

• Sequentially, where each record is taken from the next sequential physical position in the file.

• Directly by relative record number, where the record is identified by its position from the start of the file.

An externally described file has an arrival sequence access path when no key fields are specified for the file. An arrival sequence access path is valid only for the following files:

• Physical files

• Logical files in which each member of the logical file is based on only one physical file member

• Join logical files

• Views

You can use arrival sequence access paths in the following ways:

• Arrival sequence is the only processing method that allows a program to use the storage space previously occupied by a deleted record by placing another record in that storage space. This method requires explicit insertion of a record given a relative record number that you provide. Another method, in which the system manages the space created by deleting records, is the reuse deleted records attribute that can be specified for physical files.

• Through your high-level language, the Display Physical File Member (DSPPFM) command, and the Copy File (CPYF) command, you can process a keyed sequence file in arrival sequence. You can use this function for a physical file, a simple logical file based on one physical file member, or a join logical file.

• Through your high-level language, you can process a keyed sequence file directly by relative record number. You can use this function for a physical file, a simple logical file based on one physical file member, or a join logical file.

• An arrival sequence access path does not take up any additional storage and is always saved or restored with the file. (Because the arrival sequence access path is nothing more than the physical order of the data as it was stored, when you save the data you save the arrival sequence access path.)

 

Parent topic:

Describing access paths for database files

 

Related concepts

Reusing deleted records
Deleting database records